THE STEUGGLE FOE EXISTENCE 287 



Man has disturbed the natural balance of life wherever 

 he has gone. When he cuts a forest, plows a field, drains a 

 swamp, or builds a city, many kinds of life are destroyed 

 either directly or because the necessary conditions of life are re- 

 moved. Agriculture and horticulture, in fact, are attempts of 

 man to introduce new kinds of life where they did not exist. 

 The destruction of the wheat crop by insects, of cotton by 

 the boll weevil, and of apples by the codling moth are evi- 

 dences that as yet man has not succeeded in maintain ing his 

 artificial balance of life without great loss. 



316. Types of disturbance of nature's balance of life. Per- 

 haps one of the best illustrations of what occurs when plants 

 and animals are introduced into new territory is shown in 

 Australia, though the same thing may be seen in a small way 

 in almost every locality. The common rabbit was introduced 

 into Australia, and, finding favorable conditions, it multiplied 

 astonishingly. Under favorable circumstances a pair of rab- 

 bits will produce each year six litters, averaging five young 

 in each. Since rabbits feed upon vegetation, when present in 

 large numbers they competed with cattle and sheep to such 

 an extent that the grazing industry was almost destroyed in 

 some sections of Australia. 



It requires but a brief calculation to show that our previ- 

 ously acquired facts about rapid multiplication hold true for 

 these rabbits. 



Professor Sidney Dickinson says : " The original pair might 

 be responsible in five years for a progeny of over twenty mil- 

 lions. That the original score that were brought to the country 

 have propagated after some such ratio, no one can doubt who 

 has seen the enormous hordes that now devastate the land in 

 certain districts. In all but the remoter sections the rabbits 

 are now fairly under control ; one rabbiter with a pack of dogs 

 supervises stations where 100 were employed ten years ago. 

 Millions have been killed by fencing in the water holes and 

 dams during a dry season, whereby they died of thirst and 



